Const pointer to pointer to char problems

Ariesnl

I would like to manage OpenGL shaders in a more C++ and OO way
So I wanted to write a class for it..
However I run into trouble making the shader code a bit more managable..

I want to store the shader code into my class and then compile it

OpenGL expects a constant pointer to a pointer to a char "const **GLchar"
Right now I have an array of Glchar where the shadercode is stored..

Is there any good way to stuff one into the other ??

Maybe it's me but I don't see it....

#SelectExpand
  1bool OpenGLShader::Compile()
  2{
  GLchar source[m_vShaderSource.size()+2];
  vector<GLchar>::const_iterator P = m_vShaderSource.begin();
  int nIndex =0;
  while (P!=m_vShaderSource.end())
  {
      source[nIndex] = *P;
      nIndex++;
      P++;
  }
 12
  source[nIndex] ='\0';                               // <-------

  const GLchar ** pSource = &source;                  // <--------
  glShaderSource(m_nShaderIndex, 1, pSource, NULL);   // <---------
 17
 18
  glCompileShader(m_nShaderIndex);
  GLint status;
  glGetShaderiv(m_nShaderIndex, GL_COMPILE_STATUS, &status);
  if (status!=GL_TRUE)
  {
     glGetShaderInfoLog(m_nShaderIndex, 512, NULL, m_StatusBuffer);
     return false;
  }
  else
  {
      return true;
  }
 31}

Thanks...

Edgar Reynaldo

Does casting work? A const** to GLchar just means you cant change the GLchars in the array.

const ** GLChar psource = (const ** GLCchar)&source;

One thing to ask is do you need to make it a 2d array? Right now you just have an array, or a 2d array with one row. What does the shader expect?

Ariesnl

#SelectExpand
  1const GLchar* vertexSource =
  "#version 150 core\n "
  "in vec2 position;   "
  "in vec3 ColorIn;    "
  "out vec3 ColorFragment;  "
  "void main()"
  "{"
  "ColorFragment = ColorIn;"
  "gl_Position = vec4(position, 0.0, 1.0);"
  "}";

This code compiles on the graphics card so I think I need a 2D array...

Edgar Reynaldo

It doesn't just expect a concatenated string? A single one?

Arthur Kalliokoski

It compiles to one long string.

00001c60  69 6e 67 00 25 73 00 00  23 76 65 72 73 69 6f 6e  |ing.%s..#version|
00001c70  20 31 35 30 20 63 6f 72  65 0a 20 69 6e 20 76 65  | 150 core. in ve|
00001c80  63 32 20 70 6f 73 69 74  69 6f 6e 3b 20 69 6e 20  |c2 position; in |
00001c90  76 65 63 33 20 43 6f 6c  6f 72 49 6e 3b 20 6f 75  |vec3 ColorIn; ou|
00001ca0  74 20 76 65 63 33 20 43  6f 6c 6f 72 46 72 61 67  |t vec3 ColorFrag|
00001cb0  6d 65 6e 74 3b 20 76 6f  69 64 20 6d 61 69 6e 28  |ment; void main(|
00001cc0  29 7b 43 6f 6c 6f 72 46  72 61 67 6d 65 6e 74 20  |){ColorFragment |
00001cd0  3d 20 43 6f 6c 6f 72 49  6e 3b 67 6c 5f 50 6f 73  |= ColorIn;gl_Pos|
00001ce0  69 74 69 6f 6e 20 3d 20  76 65 63 34 28 70 6f 73  |ition = vec4(pos|
00001cf0  69 74 69 6f 6e 2c 20 30  2e 30 2c 20 31 2e 30 29  |ition, 0.0, 1.0)|
00001d00  3b 7d 00 00 00 00 00 00  00 00 50 c1 00 00 c0 3f  |;}........P....?|

Thomas Fjellstrom

Multiple literal strings that are one after the other get concatenated.

Edgar Reynaldo

yeah, that's kind of what I meant

Arvidsson

If you want to use a std::string: http://stackoverflow.com/questions/6047527/how-to-convert-stdstring-to-const-char

bamccaig

So basically it wants a pointer to a string? &source should be your "C string" (that is, a pointer to the beginning of the array of characters) so you may need to store that somewhere in order to take the address of that?

const GLchar * str = &source;
const GLchar ** ptr = &str;
//    Here, eat ^ that and leave us alone!

Append:

That said, a non-const pointer to a string suggests that they may wish to change it on you, which may or may not throw you for a loop... Do make sure that what you're trying is safe.

Thread #613489. Printed from Allegro.cc